FES underpowered for 18m ship?

On Wednesday, September 16, 2020 at 4:07:16 AM UTC+2, 2G wrote:
On Monday, September 14, 2020 at 11:54:00 PM UTC-7, Matthew Scutter wrote:
On Tuesday, September 15, 2020 at 7:29:17 AM UTC+2, 2G wrote:
On Monday, September 14, 2020 at 9:06:08 PM UTC-7, wrote:
Hi Eric,

I agree with you in principle, that for higher output powers, things must get bigger/heavier. However, I don't think this is the case here. The 2x batteries they use (datasheet below) are spec'd for ~40 kW discharge rate. The more realistic limiting factor might be how quickly they can dissipate heat from the batteries' internal resistance out of the battery compartment, but according to Matthew, this hasn't been a problem.
http://www.front-electric-sustainer....% 20v1.25.pdf

They would have to have a bigger inverter to handle the 40% higher input current when the batteries discharge from 4.2v-3.0v, but these ~20 kW class inverters weigh nothing (1-2 kg) compared to the batteries.
https://www.mgm-compro.com/brushless...e-controllers/

I'd be interested to hear FES's reasoning, or other owners' experiences on why the power dropoff is so significant.

Patrick Grady
I am amazed that this is even being speculated upon. How hard is it to do FES climb performance runs? You simply take off and climb until the battery (or controller) shuts down. Then, you repeat this test 5-10 times. Then you repeat that test for a different glider. Why isn't this data readily available? I can only guess that this test has been done and it is not favorable to FES.

There are many FES installations out there - if you have one, do this test and report the results.

Tom
Not readily available? It's in the flight manual. If I adjust for 5.3kWh vs 4kWh batteries and 350kg weight of the Diana 2, it's ~2000m, which matches my napkin math from partial runs.
As for why owners haven't tried it - it sounds boring...

5.3.4 Powered flight performance
5.3.4.1 Rate of climb
The maximum rate of climb is available only for a few minutes with fully charged
battery packs. As battery voltage is reduced, the maximum achievable climb rate is lower.
The average rate of climb depends mostly on the type of sailplane and its take-off weight.
Maximum attainable altitude gain that in standard atmosphere conditions depends on
the type of sailplane, its weight and aerodynamic qualities. To achieve the maximum
altitude gain, use about 15kW of power. Do not use full power as the efficiency of the
system is lower. Usually, 80-85 km/h is best for the climb with positive flap setting (the
same setting as used while thermaling). Here are rough numbers:
• 1600 m (5200 ft) for UL sailplanes at 300kg take-off weight, i.e. Silent 2 Electro
• 1400 m (4500 ft) for the 18m class sailplanes at 400kg take-off weight (without
water ballast), i.e. LAK17A FES
• 1200 m (3900 ft) for the 18m class sailplanes at 450kg take-off weight (without
water ballast); LAK17B FES, Ventus 2cxa FES, Discus 2c FES, HPH 304ES

5.3.4.2 Cruise flight
The maximum range of powered cruising flight, without the water ballast, is around
100km (62 miles), depending on lift-sink conditions.
The optimum cruise speed and flap position depend on the type of sailplane. Usually,
it is about 90 km/h (48 kts) at around 3000-3300 RPM and 4kW of power with a positive
flap setting, as used in thermals.

And you REALLY believe that? If so, I've got a bridge for sale. No, I want to see the INDEPENDENT verification of this data.

Tom

Only on RAS do you get called biased or asked if you really believe your own experiences owning and operating - couldn't make it up if you tried. Regrettably my certification as an independent standards body is still processing. My only comment on the manuals data validity would be the 4kW is not applicable to all types, the cruising flight power estimate should be scaled like the climb altitude. The heavier HpH Sharks at eGlide this year told me they were cruising with 5-6kW.

At 06:25 16 September 2020, Matthew Scutter wrote:
On Wednesday, September 16, 2020 at 4:07:16 AM UTC+2, 2G wrote:
On Monday, September 14, 2020 at 11:54:00 PM UTC-7, Matthew
Scutter
wrote=
:=20
On Tuesday, September 15, 2020 at 7:29:17 AM UTC+2, 2G
wrote:=20
On Monday, September 14, 2020 at 9:06:08 PM UTC-7,

=
wrote:=20
Hi Eric,=20
=20
I agree with you in principle, that for higher output powers,
thing=
s must get bigger/heavier. However, I don't think this is the case here.
Th=
e 2x batteries they use (datasheet below) are spec'd for ~40 kW
discharge
r=
ate. The more realistic limiting factor might be how quickly they can
dissi=
pate heat from the batteries' internal resistance out of the battery
compar=
tment, but according to Matthew, this hasn't been a problem.=20

http://www.front-electric-
sustainer.com/Manuals/FES%20BATTERY%20PAC=
K%20GEN2%2014S%2040Ah%20manual%20v1.25.pdf=20
=20
They would have to have a bigger inverter to handle the 40%
higher
=
input current when the batteries discharge from 4.2v-3.0v, but these
~20
kW=
class inverters weigh nothing (1-2 kg) compared to the batteries.=20

https://www.mgm-compro.com/brushless...rollers/33-kw-
medium=
-voltage-controllers/=20
=20
I'd be interested to hear FES's reasoning, or other owners'
experie=
nces on why the power dropoff is so significant.=20
=20
Patrick Grady=20
I am amazed that this is even being speculated upon. How hard
is it
t=
o do FES climb performance runs? You simply take off and climb until
the
ba=
ttery (or controller) shuts down. Then, you repeat this test 5-10 times.
Th=
en you repeat that test for a different glider. Why isn't this data
readily=
available? I can only guess that this test has been done and it is not
fav=
orable to FES.=20
=20
There are many FES installations out there - if you have one, do
this=
test and report the results.=20
=20
Tom=20
Not readily available? It's in the flight manual. If I adjust for
5.3kW=
h vs 4kWh batteries and 350kg weight of the Diana 2, it's ~2000m,
which
mat=
ches my napkin math from partial runs.=20
As for why owners haven't tried it - it sounds boring...=20
=20
5.3.4 Powered flight performance=20
5.3.4.1 Rate of climb=20
The maximum rate of climb is available only for a few minutes
with
full=
y charged=20
battery packs. As battery voltage is reduced, the maximum
achievable
cl=
imb rate is lower.=20
The average rate of climb depends mostly on the type of sailplane
and
i=
ts take-off weight.=20
Maximum attainable altitude gain that in standard atmosphere
conditions=
depends on=20
the type of sailplane, its weight and aerodynamic qualities. To
achieve=
the maximum=20
altitude gain, use about 15kW of power. Do not use full power as
the
ef=
ficiency of the=20
system is lower. Usually, 80-85 km/h is best for the climb with
positiv=
e flap setting (the=20
same setting as used while thermaling). Here are rough
numbers:=20
=E2=80=A2 1600 m (5200 ft) for UL sailplanes at 300kg take-off
weight,
=
i.e. Silent 2 Electro=20
=E2=80=A2 1400 m (4500 ft) for the 18m class sailplanes at
400kg
take-o=
ff weight (without=20
water ballast), i.e. LAK17A FES=20
=E2=80=A2 1200 m (3900 ft) for the 18m class sailplanes at
450kg
take-o=
ff weight (without=20
water ballast); LAK17B FES, Ventus 2cxa FES, Discus 2c FES, HPH
304ES=
=20
=20
5.3.4.2 Cruise flight=20
The maximum range of powered cruising flight, without the water
ballast=
, is around=20
100km (62 miles), depending on lift-sink conditions.=20
The optimum cruise speed and flap position depend on the type of
sailpl=
ane. Usually,=20
it is about 90 km/h (48 kts) at around 3000-3300 RPM and 4kW of
power
w=
ith a positive=20
flap setting, as used in thermals.=20
=20
And you REALLY believe that? If so, I've got a bridge for sale. No, I
wan=
t to see the INDEPENDENT verification of this data.=20
=20
Tom

Only on RAS do you get called biased or asked if you really believe
your
ow=
n experiences owning and operating - couldn't make it up if you tried.

Your command of the English language is limited obviously. You have not
been called biased - it was posed as a question - since you have and
operate a FES glider and voiced an opinion. There is a lot of BS floated
about in gliding often not backed up with substantive data that's all.

On Tuesday, September 15, 2020 at 11:25:21 PM UTC-7, Matthew Scutter wrote:
On Wednesday, September 16, 2020 at 4:07:16 AM UTC+2, 2G wrote:
On Monday, September 14, 2020 at 11:54:00 PM UTC-7, Matthew Scutter wrote:
On Tuesday, September 15, 2020 at 7:29:17 AM UTC+2, 2G wrote:
On Monday, September 14, 2020 at 9:06:08 PM UTC-7, wrote:
Hi Eric,

I agree with you in principle, that for higher output powers, things must get bigger/heavier. However, I don't think this is the case here. The 2x batteries they use (datasheet below) are spec'd for ~40 kW discharge rate. The more realistic limiting factor might be how quickly they can dissipate heat from the batteries' internal resistance out of the battery compartment, but according to Matthew, this hasn't been a problem.
http://www.front-electric-sustainer....% 20v1.25.pdf

They would have to have a bigger inverter to handle the 40% higher input current when the batteries discharge from 4.2v-3.0v, but these ~20 kW class inverters weigh nothing (1-2 kg) compared to the batteries.
https://www.mgm-compro.com/brushless...e-controllers/

I'd be interested to hear FES's reasoning, or other owners' experiences on why the power dropoff is so significant.

Patrick Grady
I am amazed that this is even being speculated upon. How hard is it to do FES climb performance runs? You simply take off and climb until the battery (or controller) shuts down. Then, you repeat this test 5-10 times. Then you repeat that test for a different glider. Why isn't this data readily available? I can only guess that this test has been done and it is not favorable to FES.

There are many FES installations out there - if you have one, do this test and report the results.

Tom
Not readily available? It's in the flight manual. If I adjust for 5.3kWh vs 4kWh batteries and 350kg weight of the Diana 2, it's ~2000m, which matches my napkin math from partial runs.
As for why owners haven't tried it - it sounds boring...

5.3.4 Powered flight performance
5.3.4.1 Rate of climb
The maximum rate of climb is available only for a few minutes with fully charged
battery packs. As battery voltage is reduced, the maximum achievable climb rate is lower.
The average rate of climb depends mostly on the type of sailplane and its take-off weight.
Maximum attainable altitude gain that in standard atmosphere conditions depends on
the type of sailplane, its weight and aerodynamic qualities. To achieve the maximum
altitude gain, use about 15kW of power. Do not use full power as the efficiency of the
system is lower. Usually, 80-85 km/h is best for the climb with positive flap setting (the
same setting as used while thermaling). Here are rough numbers:
• 1600 m (5200 ft) for UL sailplanes at 300kg take-off weight, i.e. Silent 2 Electro
• 1400 m (4500 ft) for the 18m class sailplanes at 400kg take-off weight (without
water ballast), i.e. LAK17A FES
• 1200 m (3900 ft) for the 18m class sailplanes at 450kg take-off weight (without
water ballast); LAK17B FES, Ventus 2cxa FES, Discus 2c FES, HPH 304ES

5.3.4.2 Cruise flight
The maximum range of powered cruising flight, without the water ballast, is around
100km (62 miles), depending on lift-sink conditions.
The optimum cruise speed and flap position depend on the type of sailplane. Usually,
it is about 90 km/h (48 kts) at around 3000-3300 RPM and 4kW of power with a positive
flap setting, as used in thermals.

And you REALLY believe that? If so, I've got a bridge for sale. No, I want to see the INDEPENDENT verification of this data.

Tom

Only on RAS do you get called biased or asked if you really believe your own experiences owning and operating - couldn't make it up if you tried. Regrettably my certification as an independent standards body is still processing. My only comment on the manuals data validity would be the 4kW is not applicable to all types, the cruising flight power estimate should be scaled like the climb altitude. The heavier HpH Sharks at eGlide this year told me they were cruising with 5-6kW.

Oh, so you admit that the manual is wrong - my bad!

Tom

On Friday, 18 September 2020 at 03:16:19 UTC+1, 2G wrote:
On Tuesday, September 15, 2020 at 11:25:21 PM UTC-7, Matthew Scutter wrote:


Only on RAS do you get called biased or asked if you really believe your own experiences owning and operating - couldn't make it up if you tried. Regrettably my certification as an independent standards body is still processing. My only comment on the manuals data validity would be the 4kW is not applicable to all types, the cruising flight power estimate should be scaled like the climb altitude. The heavier HpH Sharks at eGlide this year told me they were cruising with 5-6kW.
Oh, so you admit that the manual is wrong - my bad!

Tom

Are you actually interested in this subject or not?

A friend has a Ventus 2 with a FES

I asked him about time or distance endurance, and I'm inclined to believe someone I've known for over 30 years, without needing certified statements from other witnesses, plus half their curriculum vitae, as suggested by some over-argumentative type on here.

On Friday, September 18, 2020 at 2:16:26 AM UTC-7, andy l wrote:
On Friday, 18 September 2020 at 03:16:19 UTC+1, 2G wrote:
On Tuesday, September 15, 2020 at 11:25:21 PM UTC-7, Matthew Scutter wrote:


Only on RAS do you get called biased or asked if you really believe your own experiences owning and operating - couldn't make it up if you tried.. Regrettably my certification as an independent standards body is still processing. My only comment on the manuals data validity would be the 4kW is not applicable to all types, the cruising flight power estimate should be scaled like the climb altitude. The heavier HpH Sharks at eGlide this year told me they were cruising with 5-6kW.
Oh, so you admit that the manual is wrong - my bad!

Tom

Are you actually interested in this subject or not?

A friend has a Ventus 2 with a FES

I asked him about time or distance endurance, and I'm inclined to believe someone I've known for over 30 years, without needing certified statements from other witnesses, plus half their curriculum vitae, as suggested by some over-argumentative type on here.

I am VERY interested in this subject. You have me waiting with bated breath - what are your friend's results?

Tom